1. Field of the Invention
The present invention relates generally to barrier metallization layers formed upon semiconductor substrates. More particularly, the present invention relates to a low contact resistance barrier metallization layer whose surface is not susceptible to oxidation.
2. Description of Related Art
Integrated circuits are typically fabricated from semiconductor substrates upon whose surfaces are formed a multiplicity of active semiconductor regions. Within these active semiconductor regions are formed transistors, resistors, diodes and other electrical circuit elements. These circuit elements are interconnected internally and externally to the semiconductor substrate upon which they are formed through the use of conductor metallization layers which are separated by insulator layers.
As semiconductor technology has evolved, several supplementary characteristics have been found to be desirable in conductor metallization layers within integrated circuits in addition to the ability of those layers to efficient conduct electricity. Included among these supplementary characteristics are abrasion resistance characteristics, adhesive characteristics, anti-reflective characteristics and diffusional barrier characteristics.
With regard to diffusional barrier characteristics, it is often very important in advanced integrated circuit devices that conductor metallization layers not be susceptible to inhomogeneous inter-diffusion with either the semiconductor substrates with which those conductor metallization layers make contact or with adjoining conductor metallization layers with which those conductor metallization layers make contact. Inhomogeneous inter-diffusion with a semiconductor substrate may lead to formation of conductor metallization spikes into active semiconductor regions with which a conductor metallization layer makes contact. Alternatively, inhomogeneous inter-diffusion of a conductor metallization layer with an adjoining conductor metallization layer of different metallurgy composition may lead to corrosion. Since the dimensions of integrated circuit devices have continued to decrease, conductor metallization spikes and conductor metallization corrosion may readily lead to reliability and functionality concerns with advanced integrated circuits.
In order to limit inhomogeneous inter-diffusion of conductor metallization layers with silicon semiconductor substrates and adjoining conductor metallization layers with which those conductor metallization layers make contact it is common practice in the art to form a barrier metallization layer beneath and/or above a conductor metallization layer. Commonly, barrier metallization layers are formed from metals which exhibit good electrical conductivity and limited diffusivity to metals from which are formed conductor metallization layers. Metals for which it is well known that barrier metallization layers may easily be formed include titanium, tungsten, tantalum, cobalt and platinum. Of this group of metals, titanium is most commonly employed within a barrier metallization layer.
Although titanium possesses excellent characteristics with regard to inter-diffusional effects when formed as a barrier metallization layer, the use of titanium as a barrier metallization layer is not completely without problems. In particular, it is known in the art that thin titanium layers formed upon semiconductor substrates are susceptible to surface oxidation which significantly increases the contact resistance of those layers. The surface oxidation characteristics of titanium metallization layers are very important in situations where integrated circuit processing schemes require those titanium metallization layers to be exposed to an oxygen atmosphere immediately after they are formed. Such will be the case, for example, when the semiconductor processing operation immediately succeeding the formation of a titanium barrier metallization layer is of necessity not undertaken in the same reaction chamber which was used to deposit the titanium barrier metallization layer. It is thus an object of the present invention to provide a method for passivating titanium barrier metallization layers, and other barrier metallization layers which are susceptible to surface oxidation, so that semiconductor substrates upon which are formed those barrier metallization layers may be readily transferred through oxygen containing atmospheres for subsequent integrated circuit processing operations.
Methods by which thin conducting films formed upon semiconductor substrates may be modified to limit diffusional and oxidative effects are known in the art. For example, Lur et al. in U.S. Pat. No. 5,364,803 discloses a thin conducting layer which inhibits diffusion of fluorine atoms from a tungsten silicide layer of a polycide gate structure.
Desirable in the art is a method whereby surfaces of barrier metallization layers which are susceptible to oxidation may be readily and effectively passivated. Such passivation will allow for efficient transfer through oxygen containing atmospheres of semiconductor substrates upon whose surfaces reside those barrier metallization layers.